code: def ref_slice(x, start, stop, step):
      s = [
          slice(start[axis], stop[axis], step[axis])
          for axis in range(len(start))
      ]
      return x[tuple(s)]
  
file_path: nnabla/python/test/function/test_slice.py
imports: import pytest
  import numpy
  import nnabla
  import nnabla.functions
  from nbla_test_utils import list_context, function_tester
  from nnabla.testing import assert_allclose
label_desc: Use image node_id 1 for calling a global function with example usage: ref_slice(x, start, stop, step) and returns: x